The present invention relates to a paper coating composition suitably employed for improving properties of various papers such as printability, and more particularly to a paper coating composition employed for improving printability, plasticizer resistance, oil resistance, solvent resistance and water resistance of a heat sensitive recording paper.
A recording process utilizing heat has been utilized more and more because it is advantageous in comparison with a conventional recording process which requires inks, development and fixed process. Particularly, the thermal recording paper having a heat sensitive layer in which a color forming material such as Crystal Violet lactone and a color developing material such as a phenol compound are included and they are thermally reacted to develop a color, is highly estimated and has been put to practical use.
As a binder for the above-mentioned color forming material and color developing material, a water-soluble binder such as polyvinyl alcohol (hereinafter referred to as "PVA") is widely employed. However, the PVA has defects that dust of PVA may make dirty a thermal print head during a long time recording and that the printed letter disappear and the recording paper grows sticky in contact with water or plasticizers. Recently, in order to solve the problems, there has been proposed a recording paper in which acetoacetyl group-containing PVA is employed as a binder of the heat sensitive layer [Japanese Unexamined Patent Publication (Tokkyo Kokai) No. 181687/1983], a recording paper in which a protective layer composed of a carboxylic acid-modified PVA or acetoacetyl group-containing PVA is placed on the heat sensitive layer (Tokkyo Kokai No. 106995/1984), and the like, but there is a room for various improvements.
Particularly, the increase of the color density is not always remarkable in addition to demands of more improvements in the plasticizer resistance, oil resistance and solvent resistance. Also there has been requested a paper which does not cause the printed letters to disappear for a long time, even if the recording papers are in contact with plastic films or sheets including a large amount of plastisizer.
An object of the invention is to provide a paper coating composition which can solve the abovementioned problems.
The above and other objects of the present invention will become apparant from the description hereinafter.